Article

Commentary: Shedding Pounds

Lightweighting. You’ll hear this word a lot in the next few years. It refers to engineering efforts to slice weight from just about every single component on a truck or tractor in the name of fuel efficiency. And where better to start than with a truck’s backbone, its frame?

Who would have guessed that a monocoque truck chassis could be built? It’s been done by Canadian company Magna International and its European subsidiary, Magna Steyr.

(Monocoque is a type of construction where the outer skin carries all or a major part of the stresses, like an airplane fuselage.) Magna’s body and chassis unit, Cosma International, is also much involved in the Peterbilt Model 579 and Kenworth T680 introduced last year.

ADVERTISEMENT

I first learned about the chassis through a friend of mine in India. Eliott Lobo had written an excellent piece about it in Autocar Professional. Magna displayed its lightweight steel frame for the first time at last fall’s IAA show in Germany.

Intended for use in European long-haul transport but with possible applications here, at 1,312 pounds, it weighs a very significant 30% less than conventional frames.

It was developed by Engineering Center Steyr (ECS), Magna Powertrain’s truck research and development operation, in co-operation with Cosma. And it’s ready for market.

“The significant reduction in weight has been achieved by replacing the standard-type chassis frame with a unique steel monocoque structure, while maintaining the same or better technical performance,” says Franz Dorfer, general manager of ECS.

As Eliott wrote, engineers long ago exhausted any weight-reduction potential in the good old C-profile steel frame with crossmembers, which goes back to the ladder-type chassis in Gottlieb Daimler’s Phoenix in 1896. The use of high-strength steels became their only real option.

Aluminum and carbon fiber have also been explored, but so far nobody’s come up with a way to beat their cost and durability limitations. If anything is to be done, it’s going to be on the design side, not materials.

Enter Gregor Schwarz of ECS, who came up with the monocoque idea and wrote his thesis on it while a student at the Graz University of Technology in Austria.

The frame he designed is for a 4x2 tractor with a 142-inch wheelbase. It actually combines modular and monocoque design concepts and is built almost entirely of S355 structural sheet steel. It forces no change to the typical European powertrain and suspension package of leaf springs up front and air springs at the rear.

There are four modules: a cast front-end module, a double-walled front-axle module, a single-wall monocoque middle module, and a rear-axle module with outer and inner shells. The monocoque, which accounts for the dramatic reduction in weight, has a wall thickness that’s only about 15% of the standard ladder frame. And the overall structure has a torsional stiffness claimed to be 10 times that of a ladder frame.

Magna Steyr is shopping its idea around Europe, but it could be applied to North American needs as well. Schwarz is convinced he can attack other chassis components – fifth wheels, for example – and ultimately shave as much as 1,543 pounds off the weight of a European tractor. Wow.